Method for driving a vehicle with manually shifted transmission, automatic transmission or continous transmission on streets with low friction value

ABSTRACT

A method for operating a motor vehicle with a manual transmission, a multi-ratio automatic transmission or a continuously variable transmission, on a road with a low friction coefficient, the engine torque is reduced or, as the case may be, decreased, which leads to a reduction of the wheel drive torque without changing the starting gear ratio.

The present invention relates to a method for operating a motor vehiclewith a manual transmission, multi-ratio automatic transmission or acontinuously variable transmission on roads with a low frictioncoefficient according to the preamble to claim 1. The invention relatesespecially to a driving program, which will improve the drivingsituation on roads with a weather-related reduced friction coefficient,such as on ice or snow, and especially during starting.

In some vehicles, which contain automatic transmissions, a winterprogram can be pre-selected with a switch or a push button. Hereby, thewinter program for multi-ratio automatic transmissions according to thestate of the art differs from the standard driving program especially inthat the starting takes place in the second or third gear in such a waythat, because of the longer starting gear ratio with the same gas pedalposition and engine speed, a reduction of the drive torque on the wheelcompared to the standard program will be achieved. At higher gas pedalvalues, according to the state of the art the full driving performancewill be made available through downshifting.

In a continuously variable transmission (CVT transmission) without aclutch on the output side no change can be made to the gear ratio of thevariable speed gear when the vehicle is standing still since thevariable speed gear disk sets are not turning. Therefore, a longerstarting gear ratio also cannot be achieved within the scope of a winterprogram for reducing the drive torque on the wheel.

The present invention is based on the task of establishing a method foroperating a motor vehicle with a continuously variable transmission onroads with a low friction coefficient (winter driving program), whichenables the reduction of the drive torque on the wheel. Additionally,the method according to the invention should also be suitable forvehicles with a manual transmission, a multi-ratio automatictransmission or automatic shift manual transmission.

This task will also be solved by the characteristics of the patent claim1. Additional designs and advantages according to the invention are alsodisclosed in the dependent claims.

Accordingly, for operating a motor vehicle comprising a continuouslyvariable transmission on roads with a low friction coefficient it issuggested to reduce the engine torque or, as the case may be, diminishit, which will lead to the reduction of the wheel drive torque, alsowithout changing the starting gear ratio. This measure can beadvantageously used also for vehicles with a multi-ratio automatictransmissions and manual transmissions.

According to the invention, the decrease of the engine torque can beaccomplished directly in the motor-actuated control orvia engagement inthe engine on the part of the transmission. In contrast to the state ofthe art the concept according to the invention can be utilized forreducing the wheel drive torque when driving forward or in reverse.

The invention will be described in greater detail in the following byway of example of the enclosed figures.

FIG. 1 is a block diagram of a first variant of the method according tothe invention;

FIG. 2 is a block diagram of a second variant of the method according tothe invention;

FIG. 3 is the course of the engine torque as a function of the enginespeed and the gas pedal value within the scope of the standard drivingprogram; and

FIG. 4 is the course of the engine torque as a function of the enginespeed and the gas pedal value within the scope of the standard drivingprogram according to the invention.

FIG. 1 represents a first variant of the method according to theinvention. Hereby, within the scope of the winter driving program, thevalues of the engine torque as a function of the engine speed and thegas pedal value (engine torque M=f (gas pedal value, engine speed)) aremodified such that they are reduced in comparison to the standardprogram. Within the scope of an advantageous further development, thevalues of the engine torque at high gas pedal values correspond to thevalues of the standard driving program.

According to the variant of the method according to the invention shownin FIG. 2, the engine torque on the road with a low frictioncoefficient, that is to say, in the winter driving program, will bemodified or, as the case may be, reduced in comparison to the standarddriving program, which is dependent on the engine speed, the gear ratio,the vehicle speed, and or the gas pedal value, by a factor k. In thiscase it can also be anticipated that at high gas pedal values the enginetorque will not be reduced (the factor k assumes the Value 1).

Represented in FIG. 3 is the course of the engine torque in the standarddriving program as a function of the engine speed and the gas pedalvalue. From the comparison with the course of the engine torque in thewinter driving program shown in FIG. 4, it becomes apparent that throughthe inventive engine engagement the engine torque is significantlyreduced at the same engine speed and the same gas pedal value, whichleads to improved starting conditions. Additionally it will becomeobvious from the comparison of the two figures that at high gas pedalvalues the engine torque values will remain the same. The reduction ofthe engine torque can be accomplished, as has been explained already,either directly in the motor-actuated control or by means of engagementin the engine on the part of the transmission. Furthermore, according tothe invention, several winter driving programs can be provided, whichreduce accordingly the engine torque in dependence on the friction valueof the road. That means that, in this case for example, the factor kcould also depend on the road friction coefficient.

1-6. (canceled)
 7. A method for operating a motor vehicle with one of amanual transmission, multi-ratio automatic transmission or acontinuously variable transmission on a road having a low frictioncoefficient, an engine torque is reduced or, as the case may be,decreased, which leads to a reduction in a wheel drive torque withoutchanging a starting gear ratio:
 8. The method according to claim 7,wherein reduction of the engine torque is carried out directly in one ofa motor-actuated control or by engagement in an engine on the part ofthe transmission.
 9. The method according to claim 7, wherein values ofthe engine torque as a function of the engine speed and a gas pedalvalue are modified in such a way that they are reduced in comparisonwith the standard program.
 10. The method according to claim 7, whereinengine torque on the road with a low friction coefficient or, as thecase may be, in a winter driving program as compared to a standarddriving program, is modified or, as the case may be, reduced by a factork, which is dependent on one or more of an engine speed, a gear ratio, avehicle speed and a gas pedal value.
 11. The method according to claim7, wherein engine torque values at a high gas pedal value correspond tovalues of a standard driving program.
 12. The method according to claim7, wherein dependence on a road friction coefficient several reductionlevels of the engine torque are provided, which will reduce the enginetorque accordingly.
 13. A method for operating a motor vehicle havingone of a manual transmission, multi-ratio automatic transmission or acontinuously variable transmission, on a surface having a low frictioncoefficient, the method comprising the step of: reducing an enginetorque thereby leading to a reduction in a wheel drive torque withoutchanging a starting gear ratio.
 14. The method according to claim 13,further comprising the step of reducing the engine torque directly inone of a motor-actuated control or by engagement in an engine on thepart of the transmission.
 15. The method according to claim 13, furthercomprising the step of modifying values of the engine torque as afunction of engine speed and gas pedal in such a way that the values arereduced in comparison with a standard program.
 16. The method accordingto claim 13, further comprising the step of modifying engine torque whenthe vehicle is in a winter driving program as compared to a standarddriving program, by a factor k, which is dependent on one or more of anengine speed, a gear ratio, a vehicle speed and a gas pedal value. 17.The method according to claim 13, further comprising the step ofcorresponding engine torque values at a high gas pedal value to valuesof a standard driving program.
 18. The method according to claim 13,further comprising the step of providing dependence on a road frictioncoefficient several reduction levels of the engine torque, which willreduce the engine torque accordingly.